Countercurrent liquid-liquid extraction techniques in which one material is transferred from one solution to another by countercurrent contacting of the two liquid phases has long been used as a laboratory and industrial process. A variety of liquid-liquid contacting apparatus have been proposed for the purpose of carrying out such extraction techniques. For the most part, such apparatus is designed to have the contact area, time of contact and the intimacy of contact between the solutions as high as possible with the expenditure of a minimum amount of energy. In order to achieve the requisite high contact area and intimacy of contact, conventional extraction columns have been filled with foreign objects of practically every reasonable size and shape such as, metal rings, rods, saddles, glass rings, Raschig rings, porcelain rings, Berl saddles, wire mesh packing, and the like. Other types of packing or contact elements are disclosed in U.S. Pat. No. 3,585,005 to Coggan.
The Coggan patent relates to a liquid-liquid contactor which comprises a hollow member through which in operation immiscible or partially miscible fluid phases are arranged to flow. Within the hollow member, at least one surface is preferentially wetted by one of the phases and is so arranged that substantially all of that phase during passage through the contactor flows on the surface in the form of a film. The hollow member is actually a column which may include as contact elements a number of vertically-arranged plates made alternately of glass and PTFE coated stainless steel. The plates are generally flat plates which may include baffles, containing holes. Alternatively, the flat plates may be replaced by a series of concentric tubes of increasing diameter or a plurality of spaced apart parallel rods. All of these contact elements are solid in nature and are not designed to sorb the solutions flowing by or through these elements.
U.S. Pat. No. 2,472,578 to Ferris et al discloses a method of contacting a liquid with a gas or with other immiscible or partially immiscible liquids. It is indicated that one of the fluids is formed into a guided free film and such film is intimately contacted with a second fluid without rupturing the guided free film, and the fluids are thereafter separated. The apparatus employed in carrying out such method comprises a vessel or chamber which includes a plurality of vertical rods or guides suitably spaced from one another for increasing the surface of contact between the fluids. The rods or guides are capable of being wetted by one of the fluids to form a plurality of thin films extending between the rods. It is indicated that the rods or guides may be made of metal, plastics, carbon or ceramic material and are rendered wettable by oil. The rods or guides do not sorb fluids but are merely wetted thereby.
U.S. Pat. No. 2,091,917 to Fenske et al discloses apparatus for the fractionation and/or extraction of mineral oils. The apparatus includes a column, a plurality of attenuated packing members vertically arranged in the column, the packing members being separated from each other. The packing members may comprise lengths of chain.
It has now been found that the efficiency of many of the prior art continuous countercurrent liquid-liquid extraction techniques and apparatus may be increased by employing as the packing material a plurality or bundle of elongated fibrous strands which are capable of sorbing at least one of the solutions to be processed, usually the heavier solution, in capillaries or interstitial spaces of the fibrous strands thereby increasing the contact surface of the solution. This action presents a greater contact surface of the heavier solution to the lighter solution and thereby produces excellent extraction efficiences.
The terms "sorb", "sorbed", "sorbing" and the like as employed herein refer to the filling of the capillaries of the individual strands of the plurality of elongated fibrous strands comprising the packing material of the invention with solutions by virtue of absorption, adsorption and/or other surface active forces.